contrib.comments is already a bit bloated and I'd be wary of adding more settings, especially considering the fact that it already is possible to have entirely customised comment models.

Your proposal is not acceptable as-is because there would be a confusion from a developer's perspective as to what the setting applies to (i.e. to the default ordering, to the feeds, or both?). I also think that accepting 'reverse' isn't ideal -- if anything, you'd only allow to provide an explicit list/tuple of fields.

Marking as DDN for now to leave a chance for a nice API to be proposed. If no clean API can emerge, then this would be a wontfix.